STRESS CORROSION CRACKING OF SINGLE CRYSTALS OF SOME AUSTENITIC STAINLESS STEELS
CARNEGIE INST OF TECH PITTSBURGH PA
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Fe-20Cr-20Ni, Fe-20Cr-12Ni, and commercial type 304 stainless steel single crystals were loaded in tension in boiling 42 MgCl2 solution. The commercial type 304 stainless steel cracked or fractured in 4 to 17 hours, the Fe-20Cr-12Ni in 16-62 hours, and the Fe-20Cr-20Ni in 70-170 hours. The crack in all three alloys nucleated over from elongated pits formed when portions of slip lines were attacked by the solution. The crack plane of the Fe-20Cr-20Ni specimens followed the 100 plane with the highest normal stress upon it. This is believed to be the first time that brittle cracks have been noted to follow a particular crystallographic plane in fcc material. Electron diffraction patterns made of the corrosion product from a Fe-20Cr-20Ni crack face showed that it may be a chromium-iron oxide. Colorimetric analysis of the corrosion solution showed an increase in nickel during the test. The general crack plane in type 304 and Fe-20Cr12Ni specimens was approximately normal to the tensile axis. Electron micrographs of the fracture surface on a type 304 specimen revealed possible crystallographic steps on a small scale. It is proposed that the mechanism for this process probably consists of two stages 1 a slow electrochemical crack initiation and re-initiation step and 2 a rapid mechanical fracture step.
- Metallurgy and Metallography
- Properties of Metals and Alloys